The invention relates to Medium Access Control (MAC) protocols in CSMA networks.
Shared medium access networks use some type of medium access control protocol to control access to the physical medium. That shared medium access mechanisms may be polling, Time Division Multiple Access (TDMA), Carrier Sense Multiple Access (CSMA), or some other shared access protocol. Polling uses a centrally assigned master station to periodically poll other (slave) stations, giving those other nodes explicit permission to transmit on the medium. In the TDMA protocol, a network master broadcasts a frame synchronization signal before each round of messages to synchronize clocks of all stations and, after synchronization occurs, each station transmits during a uniquely allocated time slice. In CSMA with collision avoidance (CSMA/CA), each station listens to the medium while each transmission is in progress and, after the transmission ends, waits a specified interval (or interframe gap) followed by an additional delay of one or more transmission (or contention resolution) slots based on a selected slot number before transmitting.
While distributed control schemes like CSMA are fairly efficient and flexible, they tend to exhibit poor determinacy characteristics, and are typically used for data applications only. Centralized control schemes likes polling and TDMA are more rigid and less efficient that CSMA, but work with a high degree of determinacy and thus are well suited to time-critical needs of voice and multimedia traffic.
Currently, there is a trend towards supporting different types of communication systems with one network. A single network cannot easily balance the service requirements of a variety of applications, e.g., voice, multimedia and data, using conventional MAC protocols.